Electrical contact means for hair curler having elongated annular heater

ABSTRACT

A hair curler employing a heater element formed of a conductive crystalline polymer is disclosed. The polymer, loaded with conductive particles, such as carbon black, has a positive temperature coefficient (PTC) of resistance characteristic and combines a fast warmup time with a slow cooldown time due to the phase change of amorphous polymer to crystalline upon cooling, yet does not become molten due to the sharp rise in resistance at temperatures above an anomaly temperature which limits the heat generation at elevated temperatures. Since the polymer retains its shape, no special sealing means is required to confine it as in prior art fusible wax devices. The heater element is an elongated annulus coated with conductive material on inner and outer peripheral surfaces. A sheet of conductive material is rolled into a cylinder and pressed into the bore of the annulus with a terminal extending therefrom. A sleeve of conductive material is placed about the annulus and a terminal attached to the sleeve to complete electrical connection. The outer shell of the curler extends over the terminal to provide a protected environment.

United States Patent [72] Inventor John R. DEntremont Foxboro, Mass.

[21] Appl. No. 6,094

[22] Filed Jan. 27,1970

[45] Patented Nov. 2, 1971 [73] Assignee v Texas Instruments,Incorporated Dallas, Tex.

[54] ELECTRICAL CONTACT MEANS FOR HAIR CURLER HAVING ELONGATED ANNULARHEATER 7 Claims, 4 Drawing Figs.

[52] US. Cl 219/222,

[51] Int. Cl A45d 2/36,

H05b 1/02. H05b 3/12 [50] Field of Search 219/222-226, 241, 242, 210,301, 504, 505; 132/33,36, 39 [56] References Cited UNITED STATES PATENTS2,861,163 11/1958 Asakawa..... 219/504 UX 3,243,753 3/1966 Kohler219/301 UX 3,414,704 12/1968 Flanagan 219/210 3,487,197 12/1969 DElia etal.. 219/222 3,473,004 10/1969 Block et al... 219/222 3,501,619 3/1970Buitingetal.... 3,519,792 7/1970 Solomon ABSTRACT: A hair curleremploying a heater element formed of a conductive crystalline polymer isdisclosed. The polymer, loaded with conductive particles, such as carbonblack, has a positive temperature coefficient (PTC) of resistancecharacteristic and combines a fast warmup time with a slow cooldown timedue to the phase change of amorphous polymer to crystalline uponcooling, yet does not become molten due to the sharp rise in resistanceat temperatures above an anomaly temperature which limits the heatgeneration at elevated temperatures. Since the polymer retains itsshape, no special sealing means is required to confine it as in priorart fusible wax devices. The heater element is an elongated annuluscoated with conductive material on inner and outer peripheral surfaces.A sheet of conductive material is rolled into a cylinder and pressedinto the bore ofthe annulus with a terminal extending therefrom. Asleeve of conductive material is placed about the annulus and a terminalattached to the sleeve to complete electrical connection. The outershell of the curler extends over the terminal to provide a protectedenvironment.

PATENTEUunv 2 I971 HEATING ELEMENT PTC ,HEATING ELEMENT FIG. I

R O O T M N E E R V T W N T D R N H O J BWK ATTORNEY ELECTRICAL CONTACTMEANS FOR I'IAIR CURLER HAVING ELONGATED ANNULAR HEATER BACKGROUND OFINVENTION The invention relates to hair curlers, and more particularly,to electrically heated hair curlers.

Electrically heated hair curlers have found wide market acceptance inrecent years. In general, these curlers comprise an outer cylindricalshell of a suitable polymer provided with a plurality of fingersextending outwardly from the outer peripheral surface of the shell forgrasping hair wound about the shell. These curlers are heated to adesired temperature, then taken by the user who trains hair about theperiphery. The hair is generally kept in contact with the curler for ashort period of time to effect curling of the hair. Various ways havebeen used to heat the curlers but all have certain disadvantages. Onetype of curler employs, mounted within the shell, a housing whichcontains a fusible wax. The curler is placed in heat transfer relationwith a heating element until the wax melts and is then removed from theheat source and is ready for use. However, since the wax is changed to aliquid, special precautions must be taken to insure a good seal.Further, the time which is required for the curler to be heated islonger than desirable due to the relatively low heat conductivity of thewax. The wax-filled device does, however, offer the advantage of beingan excelleht heat storage means due to the latent heat released duringpliase change of the wax from liquid to solid upon cooling. Attemptshave been made to avoid the above disadvantages by using a resistanceelement in the curler both as the heater and as the heat storage means.This avoids the liquid sealing problem but the warmup time for thedevice is still excessive since a relatively massive resistance elementmust be employed in order to store the heat for the required time afterdeenefgization. Still another disadvantage is that both of the abovetypes require current-controlling devices, such as thermostats. Further,heat distribution along the surface of the curler for both types isrelatively nonuniform with a concomitant nonuniform degree of curlingfor different sections of hair.

Thus, it is an object of the invention to obviate the disadvantages ofthe prior art curlers mentioned above.

Another object of the invention is the provision of a hair curler heaterwhich combines the functions of various components used in prior artdevices.

Yet another object is the provision of a simple, reliable, rugged haircurler device, one which provides uniform heating with no hot or coldspots. Anothei object is the provision of a hair curler heater which hasan extremely fast warmup time along with the characteristic ofmaintaining its heat for a prolonged period. Yet another advantage isthe provision of a hair curler device which needs no thermostats yetprovides close temperature control. Another object is the provision ofstructure which permits the location of electrical terminals in one endof the curler and in a recessed protected environment.

Briefly, the present invention ineets the above objects by providing ahair curler which employs a generally cylindrical tubular heatingelement located .within an outer shell in heat transfer relationtherewith. The heating element is coated on the inner and outerperipheral surfaces with electrically conductive material electricallyinsulated from one another. An inner conductor comprising an axiallyslit tubular cylinder is pressed into the bore of the heating elementand an outer conduetor comprising a tubular cylinder is received aroundthe outer peripheral surface of the heating element and is held tightlythereagainst. Terminals extend from the inner and outer conductorsthrough an electrically insulating disc. The outer shell extends axiallybeyond the terminals forming a recessed area for them.

In the accompanying drawings, in which one of the various possibleembodiments, of the invention is illustrated:

FIG. I is a cross section of a hair curler device employing an elongatedannular PTC heating element;

FIG. 2 is top plan view of the FIG. 1 device;

FIG. 3 shows a blown apart perspective of a portion of a secondembodiment of the invention utilizing another electrical contactingmeans, the curler outer shell not being shown to aid in clarity ofillustration; and

FIG. 4 shows a perspective of the second embodiment partly broken awayto show recessed terminals.

Dimensions of certain of the parts as shown in the drawings may havebeen modified and/or exaggerated for the purposes of clarity ofillustration.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scopeof, the application of which will be indicated in the followingclaims.

The heater of the present invention is made out of conductive-filledpolymer having a positive temperature coefficient of resistance above ananomaly or threshold temperature. The

heater is connected to line voltage so that current flows therethroughcausing IR heating. When the temperature rises above the anomaly point,there is a sudden and marked increase in resistance to effectively cutoff the current through the heater. Thus, this self-limiting of currenteliminated the need for a thermostat or similar control employed byprior art devices. Among the other advantages the present invention offers is that extremely fast warmup time is obtained while storing theheat for an extended period of time since the polymer acts as a heater,heat exchanger and heat sink or heat storage means. Not only does thePTC characteristic serve to limit current but it offers anotherunexpected advantage. The prior art teaches that a PTC characteristic inconductive polymers is caused by a difference in thermal expansionbetween the polymer material and the conductive filler, that is, if thepolymer has a greater thermal coefficient of expansion than theconductive-filler,particles, this would give rise to a PTC effect. Atthe temperature is raised, the polymer expands more than the conductiveparticles, thus spreading the conductive particles apart. See, forinstance, U.S. Pat. Nos. 2,978,665 and 3,243,753. However, this is not acomplete explanation since many materials, such as polyvinylchloride andpolystyrene do not exhibit a marked PTC effect even through the thermalcoefficient of expansion of the polymer is greater than that of theconductive particle.

In the present invention material is utilized in which, rather thanbeing primarily dependent upon rates of thermal expansion, the PTCeffect appears related to the phase change in polymers havingcrystalline structure. When a crystalline-type polymer, such aspolyethylene, is loaded with carbon particles, such as carbon black, thecarbon black is distributed unevenly in the polymer even with extensivemixing. Such material also includes amorphous regions and it happensthat most of the carbon particles are found in these amorphous regions.The carbon particles form large aggregates separated by crystallineregions with the separation being in the order of several hundredangstroms. Thus the polymer contains a few chains of carbon particlesforming a continuous chain through the material but the bulk of suchchains will be broken up by crystalline regions of polyethylene.Electron tunneling can occur fairly readily through thin films ofcrystalline polymer so that carbon chains broken up by crystallineregions can have conductivities approaching those of uninterruptedcarbon chains. As temperature rises, the carbon black masses separatedue to the greater thermal expansion coefficient of the polymer,increasing the difficulty of electron tunneling between carbon masseswhich offsets the increased electron tunneling effect due to temperaturerise while the crystalline regions remain intact. At temperatures belowroughly C., the resistance level is relatively flat. When thetemperature rises to the crystalline melting point, the carbon massesbecome separated by amorphous regions in which electron tunneling isvery limited, thus causing high resistance of the material. Furtherincrease of temperature causes the polymer to become semimolten whichpermits the strained carbon masses to expand in the polymer and form apartial network of carbon through the material resulting in an increasein conductivity.

Thus use of PTC polymeric resistance material not only permits combiningof several functions mentioned above but also utilizes the extraheat-storage capabilities associated with the phase change. That is,changing of the crystalline polymeric composition to the amorphous phaseupon heating stores latent heat associated with the phase change whichis released upon cooling to make a very efficient heat-storage device.

Referring now to the drawings, particularly FIGS. 1 and 2, numeralindicates generally a hair curler made in accordance with the inventionand comprises and outer, generally cylindrical, shell 12 of any suitablesynthetic resin having a plurality of fingers l4 distributed over theouter peripheral surface of the shell and extending therefrom tofacilitate holding of hair thereon. Shell 12 is formed with a closed end16 and an open end 18 to permit passage therethrough of a heaterassembly 20. Assembly 20 includes an elongated annular heating element22 formed of a conductive-filled polymer having a positive temperaturecoefficient of resistance above an anomaly or threshold temperature. Inorder to provide optimum and reliably electrical contact with thispolymeric composition, the inner and outer peripheral surfaces ofelement 22 are coated with a conductive material layers 23 and 25respectively, such as electroless nickel and tin, which are electricallyinsulated from one another and cooperate with sleeve members in closephysical connection therewith. Reference may be had to coassigned andcopending application Ser. No. 6,093 filed Jan. 27,, 1970, for furtherdetails on the method used to apply the conductive coatings to thepolymer. Sleeve 24, formed of a good electrically conductive material,such as copper, and being of a size and sufficiently thick so that wheninserted into the bore of element 22, is firmly biased against theinside surface thereof. This serves both to make electrical contact withthe conductive coating and also to support the coating and prevent itfrom peeling upon continual cycling of energization. A cap 26 isattached to sleeve 24 at one end thereof by conventional means, such asby soldering, and a pin 28, attached as by soldering, extends therefrom.It will be understood that cap 26 could be formed integrally with sleeve24 if so desired. Pin 28 extends through an aperture provided in cap 30which is received in and closes the open end of shell 12. Sleeve 32 alsoof good electrically conductive material, is placed about the outerperiphery of element 22 in tight physical contact therewith and isformed over at 34 as by crimping to enclose header 36. Header 36comprises an outer rim 38 of any convenient material, such as aluminum,surrounding an annulus 40 of dielectric material, such as polymer, whichin turn supports shelf 42. Pin 44 extends from shelf 42 and is attachedthereto by any convenient means, such as welding. To enhance theelectrical connection between pin 44 and sleeve 32, solder may be placedon surface 34 around the pin location or alternatively, shelf 42 couldbe electrically connected to rim 38 (not shown).

Element 22 is formed from a polymer material filled with conductiveparticles and having a PTC effect. The polymer is 'of a type havingcrystalline structure, such as a polyolefine, which gives rise to thePTC characteristic, as well as providing the heat storage capabilitiesassociated with the phase change from the crystalline phase to theamorphous phase. A unique advantage that this material offers is thatthe current, and hence heat generation, is limited by the markedincrease in resistance before the material melts. That is, the elongatedannulus 22 still maintains its configuration so that there is no needfor providing elaborate sealing means as in the case of devices usingfusible waxes. Yet the advantages derived from the phase change areutilized. The material is chosen so that using line voltage, resistancewill approach the level shown in FIG. 3 by the dashed lines. At thispoint, heat generation matches heat dissipation with very little changein temperature. Reference may be had to coassigned and copendingapplication Ser. No. 6,086, filed Jan. 27, I970 for further details onthe composition of the polymer material and how it is made.

Combining the heating and heat storing functions by means of the FTCpolymeric element results in a very fast warmup time along with theslow-cooling characteristics of the waxfilled devices.

Referring now to FIGS. 3 and 4, another embodiment of the invention isshown. In the FIGS. 1 and 2 embodiment, the electrical connections tothe curler are made from opposite ends through pins 28, 44. In somecases it is preferred to have both electrical terminals in the same endof the curler. As seen in FIG. 3, sleeve member 112 of suitableelectrically conductive material, such as copper, is provided with anaxial slit 114 all along its length. This may conveniently be fonned byrolling a sheet of material into a cylindrical shape. This configurationis conducive to a tighter fit of the sleeve when it is pressed into thebore of elongated annulus 22. As in the FIGS. 1 and 2 embodiment, theannulus 22 is coated in the inner and outer surface with a conductivecoating to facilitate electrical connection therewith. Sleeve 116, alsoof electrically conductive material, such as copper, is tightly fittedon the outer surface of annulus 22 to effect electrical connectiontherewith. The sleeve is formed with an inwardly extending radial flange118 on which is placed a washer 120 of electrically insulative material.Terminal 122 is attached to sleeve 116 in any suitably manner, such asby soldering, and cooperates with terminal 124 formed on sleeve 112. Adisc of electrically insulative material formed with apertures I32, 134therein for reception of terminals 122, 124 respectively is provided,and shell 136, similar to shell 12 of FIGS. 1 and 2, is pressed over theassembly. As seen in FIG. 4, shell 136 has a skirt portion 138 toprovide a recessed portion for terminals 122 and 124. Skirt 138 alsofits over base 140 on which the curler is mounted. Terminals 122 and 124are received in receptacles 142 and 144 which are connected to linevoltage. It will be understood that more than one base 140 may beprovided on a unitary support, if desired.

Thus the use of a polymer PTC heater for a hair curler results in a veryfast warmup time, yet also has a very favorably cooldown time. Itfurther obviates the need for additional thermostats to limit thecurrent since the FTC characteristic effectively limits the current flowwhen the operating temperature has been reached. Additionally, thepolymer is rugged and not subject to damage upon dropping, is extremelyuniform in heating along its surface, and is readily shaped usingconventional polymer-forming techniques. Structure is also providedwhich conveniently permits location of the terminals on one end of thecurler and which recesses the terminals in a protected environment.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also, it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense, and it is also intended that the appended claims shall cover allsuch equivalent variations as come within the true spirit and scope ofthe invention.

lclaim:

1. An electrically heated hair curler comprising a generally cylindricalouter shell of polymeric material; a generally cylindrical tubularpolymeric resistive heating element having an electrically conductivecoating on inner and outer peripheral surfaces, the coatings beingelectrically insulated from one another, the heating element beinglocated within the outer shell in good heat transfer relation therewith;

an inner conductor formed from a generally tubular cylinder ofelectrically conductive material pressed into the bore of the heatingelement and in electrical connection with the coating on the innerperipheral surface of the heating element;

a first terminal formed integrally with the inner conductor andextending axially therefrom beyond an end of the heating element;

an outer conductor formed from a generally tubular cylinder ofelectrically conductive material received around the outer peripheralsurface and held tightly thereagainst and in electrical connection withthe coating on the outer peripheral surface of the heating element, theouter and inner conductors being electrically insulated from oneanother;

a second terminal attached to the outer conductor and extending axiallytherefrom beyond the end of the heating element and aligned with thefirst terminal; and

a circular disc of electrically insulative material secured to an end ofthe outer shell and provided with terminal apertures placed so that thefirst and second terminals pass through respective terminal apertures.

2. A hair curler according to claiml in which the inner conductor is ofgreater thickness than the outer conductor and extends substantiallyalong the length of the heating element.

3. A hair curler according to claim 2 in which the inner conductor isslit along its axial length.

4. A hair curler according to claim 1 in which the outer conductor isformed with an inwardly extending radial flange and the second terminalextends from the inner portion of the flange.

5. A hair curler according to claim 4 in which a washer of electricallyinsulative material is interposed between the flange and the heatingelement.

, 6. A hair curler according to claim 1 in which the outer shell extendsaxially beyond the first and second terminals and the disc.

7. An electrically heated hair curler comprising a generally cylindricalouter shell of polymeric material; a generally cylindric tubular heatingelement having an electrically conductive coating on inner and outerperipheral surfaces, the coatings being electrically insulated from oneanother, the heating element being located within the outer shell ingood heat-transfer relation therewith;

an inner conductor formed for a generally tubular cylinder ofelectrically conductive material and having an axially extending slitpressed into the bore of the heating element and in electricalconnection with the coating on the inner peripheral surface of theheating element;

an outer conductor formed of electrically conductive material receivedon the outer peripheral surface and held tightly thereagainst and inelectrical connection with the coating on the outer peripheral surfaceof the heating element, the outer and inner conductors beingelectrically insulated from one another; and

terminal means attached to the inner and outer conductors to provideelectrical connection therewith.

* i l i l'

2. A hair curler according to claim 1 in which the inner conductor is ofgreater thickness than the outer conductor and extends substantiallyalong the length of the heating element.
 3. A hair curler according toclaim 2 in which the inner conductor is slit along its axial length. 4.A hair curler according to claim 1 in which the outer conductor isformed with an inwardly extending radial flange and the second terminalextends from the inner portion of the flange.
 5. A hair curler accordingto claim 4 in which a washer of electrically insulative material isinterposed between the flange and the heating element.
 6. A hair curleraccording to claim 1 in which the outer shell extends axially beyond thefirst and second terminals and the disc.
 7. An electrically heated haircurler comprising a generally cylindrical outer shell of polymericmaterial; a generally cylindric tubular heating element having anelectrically conductive coating on inner and outer peripheral surfaces,the coatings being electrically insulated from one another, the heatingelement being located within the outer shell in good heat-transferrelation therewith; an inner conductor formed for a generally tubularcylinder of electrically conductive material and having an axiallyextending slit pressed into the bore of the heating element and inelectrical connection with the coating on the inner peripheral surfaceof the heating element; an outer conductor formed of electricallyconductive material received on the outer peripheral surface and heldtightly thereagainst and in electrical connection with the coating onthe outer peripheral surface of the heating element, the outer and innerconductors being electrically insulated from one another; and terminalmeans attached to the inner and outer conductors to provide electricalconnection therewith.